In the United States alone, as many as 9,000 deaths annually are believed to be attributable to food-borne pathogens such as salmonella, listeria, E. coli, trichinella, staphylococcus, etc. And, for at least the years 1997-2000, there was a significant annual increase in the number of food products recalled by reason of contamination.
The hazards of natural contamination aside, intentional adulteration of the food supply—also labeled “bioterrorism”—is a widely recognized national security concern. As noted, for example, in a 2005 Congressional Research Service report for the 109th Congress: “There is widespread concern that naturally occurring pathogens such as E. coli 0157:H7, salmonella, listeria, and botulinum toxin could be used as bioterrorist weapons and could spread through the multi-link food distribution chain. Such an attack would be particularly lethal to children, the elderly, and the immune-compromised.” Donna Vogt, CRS REPORT FOR CONGRESS: food safety issued in the 109th Congress (updated Feb. 4, 2005).
Congress recognized the urgency of the crisis when it passed the Public Health Security and Bioterrorism Preparedness and Response Act (P.L. 107-188) in 2002. The act seeks to more tightly control, including through the Food and Drug administration (“FDA”), the importation and domestic processing of foodstuffs. See, e.g., http//www.cfsan.fda.gov/˜dms/defter.html.
The FDA also recognizes the risk of bioterrorism, and has proposed prevention means which would include the promulgation of further “regulations requiring companies to implement practical food defense measures at specific points in the food supply chain.” See http://www.fda.gov/oc/initiatives/advance/food/plan.html#1.1.
High-energy ionizing radiation has long been employed to treat foodstuffs such as spices, wheat, wheat flour and potatoes. More recently, such ionizing energy has begun to be employed in the treatment of foodstuffs such as meat, including poultry and pork. See, e.g., FDA (HHS) Final Rule on the Use of Irradiation in the Production, Processing, and Handling of Food, federal Register 50, 29658-29659 (July 1985). Most recently, the
FDA has approved the use of radiation to treat leafy green vegetables such as spinach and lettuce. See, e.g., http://www.mcclatchydc.com/244/story/49758.html.
The increasing use of irradiation technology has been driven by the growing incidents of sickness and death attributable to food-borne pathogens. Presently, some twenty-seven countries employ irradiation in food processing. In the United States, the FDA and the Department of Agriculture (USDA) are responsible for the establishment of regulatory guidelines respecting food irradiation processes. These guidelines specify the maximum radiation dosage to be delivered to any given food or beverage product.
High-energy ionizing radiation has long been employed to treat foodstuffs such as spices, wheat, wheat flour and potatoes. More recently, such ionizing energy has begun to be employed in the treatment of foodstuffs such as meat, including poultry and pork. See, e.g., FDA (HHS) Final Rule on the Use of Irradiation in the Production, Processing, and Handling of Food, Federal Register 50, 29658-29659 (July 1985). The increasing use of irradiation technology has been driven by the growing incidents of sickness and death attributable to foodborne pathogens. Presently, some twenty-seven countries employ irradiation in food processing. In the United States, the Food and Drug Administration (FDA) and the Department of Agriculture (USDA) are responsible for the establishment of regulatory guidelines respecting food irradiation processes. These guidelines specify the maximum radiation dosage to be delivered to any given food or beverage product.
Foodstuff irradiation is currently carried out using one or more of the following types of ionizing energy: Gamma rays; high-energy x-rays; and high energy electrons. Gamma ray sources are by far the most prevalent type of ionizing energy used in the food processing industry. These sources typically consist of large quantities of radioactive Cobalt (Co60) or Cesium (Cs137). Gamma ray sources generally have from 1 to 5 discrete energy gammas, as opposed to a continuous energy spectrum such as x-ray sources. Gamma ray sources are thus characterized as discrete energy sources. Gamma rays currently being used in food irradiation have energies in the range of from about 0.66 to about 1.33 million electron volts (MeV). Such high-energy gamma rays are able to significantly penetrate relatively dense foodstuffs, such as poultry and meats, as well as large volumes, such as palletized foodstuffs. However, gamma radiation sources suffer from a number of drawbacks which have thus far hampered the wider expansion of their use in food processing. As gamma radiation is a continuous emission (i.e., it cannot be “turned off”), harmful to humans, the source material (i.e., Co60 or Cs137) must be encapsulated in metal enclosures and stored in a deep pool of water when not in use in order to provide adequate protection for workers and the surrounding environment. This translates into the need for large, non-mobile facilities and, consequently, the need to ship foodstuffs from diverse locations to the gamma radiation source for treatment. It is, moreover, difficult to provide uniform radiation doses to a variety of foodstuffs, making the employment of gamma ray sources undesirable for a more comprehensive array of foodstuffs.
A still further drawback to conventionally employed gamma ray sources is the risk of their employment by terrorist. In February, the National Research Council of the National Academies (“NRC”) released a Congressionally-mandated report entitled “Radiation Source Use and Replacement.” In that report, which may be viewed in its entirety on the Internet at http://nap.edu/catalog.php?record id=11976, the NRC recognized that existing industrial radiation sources, including Co60 or Cs137, both of which are employed in commercial food irradiation systems, have the potential to serve as ingredients in radiological dispersal devices-so-called “dirty bombs.” See U.S. Nuclear Regulatory Commission Information Sheet. Accordingly, the NRC recommends that the U.S. government adopt policies incentivizing replacement of such high-risk radionuclide sources. This threat of “dirty bombs” is a very real one, having been recognized by the Department of Homeland Security.
Of the other conventional sources of ionizing energy, high-energy x-rays may be produced by acceleration electrons at high speeds onto a high Z (atomic number) target material, typically tungsten, tantalum, and stainless steel. Those electrons stopping in the target material produce a continuous energy spectrum of x-rays. The method of producing high energy electrons most commonly used today produces x-rays as a result of igniting an electron cyclotron resonance plasma inside an evacuated dielectric spherical chamber filled with a heavy atomic weight, non-reactive gas or gas mixture at low pressure. The spherical chamber is located inside a non-evacuated microwave resonant cavity that is in turn located between two magnets to form a magnetic mirror. Conventional microwave energy fed into the resonant cavity ignites the plasma and creates a hot electron ring from which electrons bombard the heavy gas and dielectric material to create an x-ray emission. The disclosures of U.S. Pat. No. 5,461,656, and No. 5,838,760 are exemplary. Lower energy x-rays are then filtered from this spectrum to provide a beam capable of penetrating through larger items while still maintaining a relative uniform absorption rate throughout the foodstuff being irradiated. To further ensure dosage uniformity, the foodstuff being irradiated is typically reversed in direction and orientation from the directions and orientation in which the exposure was initially made.
Conventional x-ray generating apparatus, such as the x-ray tube 100 diagrammatically shown in FIG. 1, includes a target material 102. The target material 102 is typically an element with a high Z (atomic) number, and usually comprises tungsten (Z=84), although other materials, including tantalum (Z=73), rhodium, copper, chromium, platinum, and molybdenum, as well as alloys such as rhenium-tungsten-molybdenum, are also used. X-rays are produced by accelerating electrons e− at high speeds toward this target material 102. Upon the accelerated electrons e− striking the target material 102, x-rays are produced in two forms. The first form, commonly referred to as brehmsstralung radiation, is the product of deviations in the trajectory of accelerated electrons as they pass the electron cloud surrounding the target atoms. The second form, known as characteristic radiation, is the product of the interaction between accelerated electrons and inner-shell electrons of the target atoms. More particularly, the accelerated electrons ionize inner shell electrons in the target atoms, causing outer shell electrons to move to occupy the “hole” created by the excited inner shell electron. This movement of each outer shell electron to an inner shell is accompanied by the emission of photons in the x-ray spectrum by the target atoms' electrons typically called characteristic x-rays. The majority of any given x-ray field typically comprises brehmsstralung-type radiation but does have a limited characteristic x-ray component.
Conventionally, acceleration of the electrons e− is accomplished by creating a large voltage potential across a finite space defined between a positive anode 104 comprising the target material 102, and a negative cathode 106 comprising a filament circuit (e.g., tungsten).
Alternatively, however, electron acceleration may conventionally be accomplished by having an anode maintained at ground potential, with the cathode having a high negative potential. These elements are contained in a glass vacuum enclosure 108, which is in turn contained within a metal shielding enclosure 110 used to absorb the emission therefrom of all but the desired x-rays. A suitable power source (not shown in FIG. 1) supplies the current to create the necessary electrical potential, and powers the filament circuit, which must be heated to incandescence to provide the source of accelerated electrons e−.
Conventional x-ray tubes further include cooling means, as the vast majority (approximately 98%) of radiation produced when the accelerated electrons e− strike the target is infrared (i.e., heat). Included among these cooling means is rotation of the anode 104.
Conventional x-ray tubes such as shown in FIG. 1 are further characterized by significant amounts of filtration materials 112 such as, for instance, aluminum, beryllium, glass, (and other low Z metal) to reduce the intensity of the x-ray beam 114 by absorbing lower energy photons. Further filtration also takes place as the x-ray beam exits the tube, passing first through an oil layer (not shown) and then through a beryllium (typically) window 116.
The high-energy x-rays conventionally used in the irradiation of foodstuffs have energies from 600 KeV to as high as 10 MeV rays in order to increase their penetration power. See, e.g., Report of the Consultant's Meeting on the Development of X-Ray Machines for Food Irradiation, Food and Agriculture Organization, IAEA, A-1400 (Vienna, Austria 1195. The use of high-energy x-rays is not as prevalent in the food irradiation industry primarily because conventional x-ray tubes are extremely energy inefficient. Only about 2% of energy input is translated into useful x-ray energy, the remainder being given off as heat (which must be dissipated through the expenditure of further energy). What is more, the use of high-energy x-rays requires significant shielding to protect workers from inadvertent exposure.
High-energy (i.e., up to 10 MeV) electrons, originally obtained from linear accelerators and Van de Graff generators, are characterized by the lowest penetrating power of currently-employed ionizing energy, and are therefore limited to use where the thickness of the foodstuff being irradiated is less that a few inches (3-4″) in depth.
Several major drawbacks to conventional foodstuff irradiation methodologies include the adverse impact on taste, the production of alkylcyclobutanoes (ABCs) with the irradiated foodstuffs and the radiolyctic effects associated with emissions from Gamma Ray sources. In particular, some foodstuffs evidence a marked change in flavor including an increase in bitterness associated with fruit juices, such as orange juice and grapefruit juice and a rancid fat flavor in meat products such as beef and poultry following irradiation by gamma rays and high-energy electrons because the high energy radiation destroys not only the organic pathogens and non-pathogens in the foodstuff being irradiated but also destroys the cellular membranes and the other molecules forming the foodstuff (such as flavor molecules). Other conventional beverage treatment methods, such as, for instance, heat pasteurization, likewise adversely affect the taste of these products.
Thus, it is desirable to have a means for killing organisms, pathogenic and non-pathogenic alike, in various articles, including foodstuffs, medical supplies, personal hygiene products, agricultural seeds, etc., which means are at once economical, do not adversely affect the taste of treated foodstuffs, do not produce significant amounts of ABCs, may be selectively activated and deactivated, may be employed in an “inline” processing environment so as to avoid the necessity of transporting items to a separate facility for irradiation, have none of the adverse effects of radioactive materials, alleviate public apprehension about the use of radioactive isotopes as the treating radiation, and address both the threat of bioterrorism in relation to the food supply and the threat of radiological terrorism by addressing the NRC's call to replace existing radionuclide sources that could be used in the preparation of “dirty bombs” with a radiation source (i.e., one or more x-ray tubes or x-ray sources in accordance with the invention) incapable of such application.